In some wireless communication networks, packets are delivered using the Internet Protocol, IP. This means that also traditionally circuit switched services such as voice conversation will make use of fast scheduling and it is called Voice over IP, VoIP. In a typical VoIP arrangement a voice encoder on the transmitter side encodes the speech into packets with typical speech duration of 20 ms.
Since the delay budget for the delivery of speech frames is relatively tight, there is not much time for queuing or retransmissions in the scheduler. Often in a wireless system, the cell-edge wireless devices, which are the wireless devices probably experiencing the worst channel conditions, will limit the total system performance. In this context, a cell-edge wireless device is defined as a wireless device with such high pathloss that when transmitting at its maximum powers it cannot transmit a full speech frame without retransmissions and/or segmentation. For example, a VoIP wireless device located at the cell edge may require extensive retransmissions in order to transmit a voice frame. These retransmissions will lead to increased packet delay for the wireless device, but the retransmissions will also require system resources that will reduce voice quality for other wireless devices. A potential solution to this would be to split the voice frame into a number of segments, where each segment can be transmitted with a larger success probability. But since every segment needs a Radio Link Control, RLC, and Medium Access Control, MAC, header, the transmission of many small segments will result in increased header overhead, and the link efficiency will decrease due to this. In addition to this, the load on control channels will also increase since more segments needs to be scheduled and every segment requires a new PDCCH message.